There are a number of situations such as in the mechanical testing of materials in which there is a need to apply a load to a material in a controlled manner.
According to the present invention there is provided a method of applying a load to a material comprising, positioning the material in a rig operable to apply the load, inputting data into a means to control the loading of the material, said data defining the required loading conditions,activating said control means to cause the material to be loaded, periodically determining the stress and/or strain applied to said material with sensor means associated with the rig, and varying the loading of the material by said control means in response to variations of the determined stress and/or strain from the input data.
The term "loading" as used herein is understood to means the application of a force to the material.
There is a wide range of apparatus capable of testing the mechanical properties of materials by a variety of experiments such as tensile, compression, fatigue and 3 or 4 point bending. The characteristic feature of these and other experiments used to investigate the properties of materials is that a load is applied to a specimen of the material and the response of the material to the load is measured over a period of time.
According to the present invention there is provided a method of testing the mechanical properties of a material by applying a load to the material comprising, positioning a specimen of the material in a test rig operable to apply a load to the specimen and thereby to deform or to deflect the specimen, inputting data into means to control the deformation or deflection of the specimen by the test rig, said data defining the experimental conditions for deforming or deflecting the specimen, activating said control means to cause said specimen to be deformed or deflected, periodically determining the stress and/or strain applied to the specimen as a consequence of the experimental conditions with sensor means associated with the specimen, and varying the control of the deformation or deflection of the specimen by said control means in response to variations of the determined stress and/or strain from the input data.
There are a number of known test rigs that are capable of carrying out a selection of different experiments to test the mechanical properties of a material. As indicated above, such experiments include tensile, compression, fatigue and 3 or 4 point bending carried out under constant stress, constant strain, variable stress or variable strain conditions.
A general disadvantage of the known multi-functional test rigs is that there is only limited access to the work station at which the specimen to be tested is positioned. As a consequence, it is difficult to carry out a visual inspection of the specimen during the course of an experiment, which often is useful in terms of assessing the changes occurring to the material as a consequence of the applied load. Furthermore, such limited access to the work piece prevents the positioning of equipment such as microscopes, photomultipliers and sound detection equipment in close proximity to the specimen to permit other experiments to be carried out simultaneously with the deformation of the specimen. A particular disadvantage of such multi-functional test rigs when set up to carry out 3 or 4 point bending experiments is that the under surface of the specimen is the tensile surface since the load is applied from above the specimen. As a consequence, it is not possible to carry out experiments to investigate the crazing characterisitcs of a plastics material since it is not possible to maintain a solvent in contact with the tensile surface.
According to the present invention there is provided an apparatus for carrying out 3 or 4 point bending experiments on a specimen of a material comprising, a work station comprising two outer bending members and either one or two intermediate bending members to support the specimen in a generally horizontal plane and to define the points of contact with the specimen for the 3 or 4 point bending experiments, a drive means to cause relative vertical movement between the two outer bending members and the or each intermediate bending member so that the upper surface of the specimen is the tensile surface.
It is preferred that the apparatus further comprise a frame to support the work station and the drive means, with the two outer bending members being coupled to the drive means and the or each intermediate bending member being connected to the frame.
It is also preferred that the apparatus comprise sensor means to detect the stress and/or strain applied to the specimen and display means to display the detected values of stress and/or strain.
With such an arrangement the work station may be positioned on an upper section of the support frame above the drive means so that there is generally unrestricted access to the tensile surface of the specimen, thereby permitting improved visual inspection of the specimen and simultaneous experiments based on the use of additional equipment conveniently and necessarily positioned in relation to the tensile surface of the specimen. Furthermore, with such an arrangement it is possible to carry out effective experiments to determine the crazing characteristics of a plastics material, since solvent can be maintained in contact with the tensile surface of the specimen.